docs: the record-array-field/open-array codegen bug is fixed, not open

Correct a stale note: the inline-length-word / open-array codegen issue
was resolved by the hybrid QbeGen.ArrBodyItems (per-element expansion for
small record arrays) + DeclRecTemplate/InitRecArray (runtime init for
large ones).  Covered by t_arrrecfld/t_arrrecbig/t_nestarr; the two
docs/wip repros now compile and run (exit 0 / 42).  Also correct the
handoff's P4 addendum.

docs/gaps/README.md

@@ -171,12 +171,11 @@ The `gap13` remainder (standard builtins as identifiers) and `gap14`
 
 ## Not represented by a source
 
-- **Record array field passed as an open array** — a record's inline
-  array field loses its length word when the record sits in static
-  array-of-record data, so passing the field as an `ARRAY OF …` actual
-  reads length 0 and traps.  Worked around by flattening Lower's tables;
-  the general fix and `docs/wip/nested-array-field-bug.mod` remain open
-  (see `docs/summary_l3_selfhost_fix.md`).
+- **Record array field passed as an open array** — *fixed* (hybrid
+  `QbeGen.ArrBodyItems`): small record arrays are expanded per element so
+  each inline array field's length word is in the static data; large ones
+  get a generated runtime init loop.  Covered by `t_arrrecfld`,
+  `t_arrrecbig`, `t_nestarr`; see `docs/summary_l3_selfhost_fix.md`.
 
 - ~~**Size-sensitive V3 miscompile**~~ — **root-caused 2026-10-19**: not
   size-sensitive, and not a codegen bug at all.  The `ASTDUMP` debug dump

docs/summary_l3_selfhost_fix.md

@@ -47,28 +47,27 @@ so no record field is ever passed as an open array.  This matches the
 handoff's "no arrays of records in Lower" rule (which the earlier design
 did not actually satisfy).
 
-## Deferred: general codegen fix
-
-A correct general fix was implemented and validated on the repro:
-`QbeGen.ArrBodyItems` expands record/class elements per element (reusing
-a record-field walk, with `ArrData` emitting per-element nested
-sub-descriptors via a mirrored `RecStatics`).  It fixes the repro
-(rc 0) **but inflates the compiler image past `QbeGen.sessBuf`
-(4 MiB)** — `AST.arena` is `ARRAY [0..65535] OF NodeRec` and its data
-line grows from ~40 bytes to ~2 MB.  The whole image exceeds 4 MiB and is
-silently truncated (`call ` at EOF → qbe error).
-
-Options for the follow-up:
-
-1. Emit record-array elements in a **compact interleaved form**: merge
-   adjacent zero runs into `z`, emitting only `l <len>` at each array
-   field (e.g. `NodeRec` → `l 8, z 48` per element, ~590 KB total, which
-   fits).  Needs field-size arithmetic; must match `RecItems` layout.
-2. Raise `sessBuf` (band-aid; image keeps growing).
-3. Keep flattening at the source level (as Lower now does).
-
-Also documented: `docs/wip/nested-array-field-bug.mod` (nested-array
-record field) is a related, still-open case.
+## General codegen fix — landed (hybrid)
+
+The general fix (option 1 below) was landed: `QbeGen.ArrBodyItems`
+expands record/class array elements per element when the element
+(recursively) has a nested-array field, with `ArrData` emitting the
+matching per-element sub-descriptors, so every inline array field's
+length word is in the static data.
+
+To stay inside `QbeGen.sessBuf` (4 MiB), it is a **hybrid**: only
+**small** record arrays (data ≤ 131072 bytes) are expanded per element;
+**large** ones (e.g. `AST.arena`, 65536 `NodeRec`) stay a compact zero
+blob, and their elements' inline lengths are set at run time by a
+generated init loop (`QbeGen.DeclRecTemplate` + `QbeGen.InitRecArray`,
+driven from `Lower`).  Plain record arrays (no nested-array field) stay
+a compact zero blob, so `AST.arena` does not balloon.
+
+Fixed and covered by `compiler/tests/t_arrrecfld.mod` (small),
+`t_arrrecbig.mod` (large), `t_nestarr.mod` (nested) and `t_recarr.mod`
+— all run green, and `docs/wip/arrrec-field-openarray.mod` /
+`docs/wip/nested-array-field-bug.mod` now compile and exit 0 / 42.  No
+open codegen case remains here.
 
 ## Latent fragility — root-caused (2026-10-19)
 
@@ -93,6 +92,5 @@ and the gate fails), and the fixpoint is byte-identical across the
 four size-changing commits of 2026-10-19.
 
 (The separate record-array-field / open-array codegen issue is described
-above; the deferred general `ArrBodyItems` fix and
-`docs/wip/nested-array-field-bug.mod` remain open — that is a *distinct*
-bug from the `ASTDUMP` one.)
+above and is **fixed** — that was a *distinct* bug from the `ASTDUMP`
+one, resolved by the hybrid `ArrBodyItems`/`InitRecArray` fix.)